An electrical current detection device for measuring a current is configured by a sensor element such as a shunt resistor, a Hall element, and an electrical current detection device for estimating a current value from a detection signal of the sensor element. Concretely, the Hall element outputs the voltage as a detection signal corresponding the current, and then the current can be estimated from the detected voltage. Especially, in a case of using the shunt resistor, there is a feature that the electrical current detection device can be configured by comparatively simple circuits.
Also, a power supply device equipped with an assembled battery configured by a plurality of battery cells, has a state monitoring unit for monitoring states of the battery cells in order to avoid abnormal states of over-charge or over-discharge in the battery cells. The state monitoring unit includes a voltage detection circuit for detecting a voltage in each of the battery cells, a current detection circuit for detecting a charge-discharge current of the assembled battery, and a temperature detection circuit for detecting an ambient temperature (environmental temperature), a temperature of the assembled battery, or the like. In the same as the above-mentioned electrical current detection device, the current detection circuit estimates a charge-discharge current of the assembled battery, by using the detection signal from a sensor element for detecting the charge-discharge current of the assembled battery. Since this type of the power supply device monitors states of the battery cells based on the detection data including the current, it is not preferable that the power supply device is used, for example, in a condition where the current cannot be detected.
To resolve such a problem, as the configuration which effectively prevents a breakdown of the electrical current detection device, a power supply device equipped with a plurality of sensor elements for detecting a current through the same current passage, is proposed (Patent Literature 1). Concretely, the power supply device of Patent Literature 1 has a shunt resistor including two resistor elements, and two detection signals are outputted corresponding to a current flowing through the shunt resistor, and then the current flowing the shunt resistor is estimated based on one of the two detection signals. In this configuration, as long as either or both of the two detection signals are detected, as the current can be estimated, the breakdown of the power supply can be suppressed. Additionally, in the power supply device of Patent Literature 1, as the shunt resistor structure is the integral structure of the two resistors, the structure of the sensor element is simplified.